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Role of internal stresses in fracture behavior of engineering composites

Conference ·
OSTI ID:10188127
Microstructure and fracture behavior of SiC(f)/Si{sub 3}N{sub 4} matrix composites, and of Ag-particulate/YBa{sub 2}Cu{sub 3}O{sub x}[YBCO] superconductor matrix composites, together with internal residual strains in composite constituents, have been evaluated as a function of reinforcing-fiber, particulate content, and processing variables. Residual strains were measured by neutron diffraction with the Intense Pulsed Neutron Source and Powder Diffractometer at Argonne National Laboratory. Internal radial strains on SiC fibers in SiC(f)/Si{sub 3}N{sub 4} composites decreased from 0.0015 at 8.4 vol.% fibers to 0.0010 at 23.3 vol.% fibers. This decrease in radial strain with increasing fiber volume fraction is expected to reduce frictional and hence interfacial sliding stresses between SiC fibers and Si{sub 3}N{sub 4} matrix; this is in agreement with interfacial shear strengths measured by the fiber pushout technique. Similar relationships between residual strain and interfacial shear strength was observed for composites hot isostatically pressed (HIPed). For YBCO-AG composites, tensile strain in the Ag phase was as high as 0.085%, whereas compressive strain in the YBCO phase reached 0.09%. The presence of compressive strain (stress) improved the strength of YBCO from 200 to 223 MPa. Implications of the effects of residual stresses on interfacial characteristics and resulting composite mechanical properties and fracture behavior will be discussed.
Research Organization:
Argonne National Lab., IL (United States)
Sponsoring Organization:
USDOE, Washington, DC (United States)
DOE Contract Number:
W-31109-ENG-38
OSTI ID:
10188127
Report Number(s):
ANL/ET/CP--82224; CONF-9410184--3; ON: DE95001106
Country of Publication:
United States
Language:
English